1. Field of the Invention
This invention relates generally to a multiple frequency band and/or multiple polarization mode antenna system having multiple antenna subsystems for radar, remote sensing, communications or a combination of various applications, where each antenna subsystem (each band or mode) shares a common aperture and boresight, More particularly, the present invention relates to multi-band/dual-polarization radar antenna system for a radar seeker that employs properties of frequency selective surfaces to allow several antenna subsystems to use a common aperture and boresight.
2. Discussion of the Related Art
Many applications exist for the transmission and reception of signals for both radar and communications purposes. Radar systems are known to provide target tracking and acquisition. Various antenna configurations known in the art provide dual-band and dual-polarization functions for the radar systems. U.S. Pat. No. 5,451,969 issued to Toth et al. entitled "Dual Polarized Dual Band Antenna" discloses an antenna configuration for such an application.
Modern, advanced tactical missiles are typically equipped with a radar seeker to provide target acquisition and tracking functions, and also are outfitted with electronic-counter-counter-measure (ECCM) devices to mitigate known electronic-counter-measures (ECM), such as cross-eye, cross-polarization, towed decoy and terrain bouncing jamming, to achieve a desirable "hit-to-kill" ratio. To counter these existing and potential future threats, radar sensors with enhanced capabilities which can successfully function in an advanced ECM threat environment are needed for the next-generation advanced tactical missiles. To achieve this goal, an advanced multi-band and polarization-diversified radar antenna architecture is necessary.
Advanced multi-band/polarization-diversified radar antenna architectures possess many advantages over conventional antenna architectures. These advantages include providing up to four separate antennas sharing a single common aperture and operating at four different frequency bands with full aperture RF performance; providing any selected polarization for each antenna; providing a co-boresight for all four antenna beams; providing a compact volume/size for missile applications; providing enhanced anti-jamming capability in general; providing additional ECCM enhancements; and providing precision profiling of targets by high band channels with higher resolution during the terminal homing phase.
To make a multi-band/dual-polarization radar system, it is necessary to provide a multi-band/polarization-diversified antenna system which shares a given aperture with minimum antenna performance degradations in the presence of each different antenna. The use of frequency selective surfaces (FSS) offers a practical technique for integrating different frequencies and/or polarization modes in a multi-band/polarization-diversified antenna system. Properly designed FSS devices are able to pass signals at one frequency band and reflect or block signals at another frequency band, and are non-discriminative to various polarization modes, both linear and circular types, to both designed frequency bands. Antenna systems employing these types of FSS have been identified in the art, and are shown, for example, in U.S. Pat. Nos. 5,949,387 entitled "Frequency Selective Surface (FSS) Filter For An Antenna"; 5,497,169 entitled "Wide Angle, Single Screen, Gridded Square-Loop Frequency Selective Surface For Diplexing Two Closely Separated Frequency Bands" and 5,373,302 entitled "Double-Loop Frequency Selective Surface For Multi Frequency Division Multiplexing in A Dual Reflector Antenna".